Optical transceiver with variable data rate and sensitivity control

ABSTRACT

An optical communications system includes a modulator/demodulator (modem) to transmit outgoing communications data and to receive incoming communications data in a transceiver. A main detector is coupled to the modem to convert an optical signal representing the incoming communications data to an electrical signal for the modem. An adaptive data rate processor monitors the electrical signal from the main detector to determine a current power level for the optical signal. The adaptive data rate processor dynamically adjusts a data rate of the modem based on the determined current power level of the optical signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims priority to,co-pending U.S. patent application Ser. No. 16/022,329, filed 28 Jun.2018, which is a continuation of U.S. patent application Ser. No.14/132,992, filed 18 Dec. 2013, which issued as U.S. Pat. No. 10,038,497on 31 Jul. 2018.

TECHNICAL FIELD

This disclosure relates to optical communications, and more particularlyto an optical transceiver system and method that dynamically varies thecommunications data rate of the system based upon detected optical powerlevels.

BACKGROUND

Free space optical communication has attracted considerable attentionrecently for a variety of applications. Atmospheric turbulence candegrade the performance of free-space optical links (e.g., tens ofdecibels), particularly over ranges of the order of 1 km or longer. Lackof homogeneity in the temperature and pressure of the atmosphere, forexample, can lead to variations of the refractive index along theoptical transmission path. Such refractive index variations candeteriorate the quality of the received image and can cause fluctuationsin both the intensity and the phase of the received optical signal.These fluctuations, which are also referred to as fading, can lead to anincrease in the link error probability, limiting the performance ofoptical communication systems.

For optical communications systems design, the effects of fading shouldbe accounted for to ensure reliable system operation. In suitableatmospheric conditions, received optical signals may be strong whichcould saturate a photodector at the optical receiver. In pooratmospheric conditions, weak optical signals need to be boosted overbackground noise levels in order to properly distinguish transmitteddata from noise. Thus, optical systems needs to be designed to operateover a fairly large dynamic power range accounting for strong signalstrength under optimal conditions and weak signal strength under poorconditions.

SUMMARY

This disclosure relates to optical communications systems. In oneaspect, an optical communications system includes amodulator/demodulator (modem) to transmit outgoing communications dataand to receive incoming communications data in a transceiver. A maindetector is coupled to the modem to convert an optical signalrepresenting the incoming communications data to an electrical signalfor the modem. An adaptive data rate processor monitors the electricalsignal from the main detector to determine a current power level for theoptical signal. The adaptive data rate processor dynamically adjusts adata rate of the modem based on the determined current power level ofthe optical signal.

In another aspect, an optical communications system includes amodulator/demodulator (modem) to transmit outgoing communications dataand to receive incoming communications data in a transceiver. A maindetector is coupled to the modem to convert an optical signalrepresenting the incoming communications data to an electrical signalfor the modem. An auxiliary detector detects a power level of theoptical signal and generates an electrical output signal representingthe power level. An adaptive data rate processor monitors the electricaloutput signal from the auxiliary detector to determine a current powerlevel for the optical signal. The adaptive data rate processordynamically adjusts a data rate of the modem based on the determinedcurrent power level of the optical signal.

In yet another aspect, an optical communications method includesdetecting a current power level of a received optical signal in anoptical transceiver. The method includes determining if the currentpower level of the received optical signal has changed from a previouspower level. The method includes adjusting a data rate for the opticaltransceiver if the current power level of the received optical signalhas changed from the previous power level. The method also includesadjusting a sensitivity level of at least one detector in the opticaltransceiver if the current power level of the received optical signalhas changed from the previous power level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of an optical communications system thatdynamically varies the communications data rate of amodulator/demodulator (modem) based upon detected optical power levels.

FIG. 2 illustrates an example diagram of received optical power levelsthat can be monitored by an adaptive data rate processor to adjust adata rate or a sensitivity level of an optical transceiver.

FIG. 3 illustrates an example of an optical communications system thatemploys separate transmitter and receiver paths to dynamically vary thecommunications data rate of a modulator/demodulator (modem) based upondetected optical power levels.

FIG. 4 illustrates an example of an optical communications system thatemploys an auxiliary detector to dynamically vary the communicationsdata rate of a modulator/demodulator (modem) based upon detected opticalpower levels.

FIG. 5 illustrates an example of an optical communications method thatdynamically varies the communications data rate of an opticaltransceiver based upon detected optical power levels.

DETAILED DESCRIPTION

This disclosure relates to an optical transceiver system and method thatdynamically varies the communications data rate of amodulator/demodulator (modem) based upon detected optical power levels.Atmospheric conditions are continuously monitored to determine thestrength of received optical signals. During clear line-of-sightconditions between optical transmitter and receiver, optical signalstrength can be stronger (e.g., higher signal-to-noise) than when fadingconditions cause the signal strength to degrade. An adaptive data rateprocessor periodically monitors incoming signal strength and candynamically increase or decrease communications data rate of the modembased on detection of the current signal conditions. For example, understrong signal conditions, data rate can be increased to accommodatefavorable conditions and improve communications throughput. When weaksignal conditions are detected (e.g., due to fading, pointing,acquisition, tracking (PAT) misalignment, and/or distance limitations),data rate of the modem can automatically be reduced by the adaptive datarate processor to mitigate loss of data.

In one example, a main detector can be employed to detect incoming powerlevel conditions and to also receive optical communications data for themodem. In addition to adjusting the data rate of the modem based on thedetected power level, the adaptive data rate processor can alsodynamically increase or decrease the sensitivity of the main detector.This can include applying differing reverse bias voltage levels to anavalanche photodiode to increase or decrease detector sensitivity andfurther enhance communications performance (e.g., increase detectorsensitivity for weak signal conditions). Thus, when power level changesare detected, the adaptive data rate processor can dynamically changethe data rate at which the modem operates and/or dynamically change thesensitivity of the optical transceiver system. Such data rate changescan be communicated via a negotiation protocol with a remote transceiverfor synchronous data rate adjustments (e.g., send a header packetindicating data rate change to remote transceiver). In another example,each transmitter in the local and remote communications loop canasynchronously adjust the respective data rate (e.g., for every 10 db inpower level detected, increase or decrease data rate by predeterminedamount based on detected power level change).

In yet another example, an auxiliary detector can be employed to detectpower level changes by the adaptive data rate processor while the maindetector is utilized to receive optical data and convert the opticaldata to electrical data at the modem. The adaptive data rate processorcan dynamically adjust the data rate of the modem based on the signaldetected from the auxiliary detector. In this example, the adaptive datarate processor can also dynamically adjust the sensitivity of both themain detector and the auxiliary detector to further improvecommunications performance. Various transceiver configurations can beprovided to both transmit and receive optical data. A method is alsoprovided for dynamically adjusting transceiver data rate and/ortransceiver sensitivity based on detected optical conditions.

FIG. 1 illustrates an example of an optical communications system 100that dynamically varies the communications data rate of amodulator/demodulator (modem) 110 based upon detected optical powerlevels. The system 100 includes receiver optics 120 that can includetelescopic components and filters for transmitting and/or receiving anoptical signal via a line-of sight optical path (or substantiallyline-of-sight). Output from the receiver optics 120 is fed to one ormore optical couplers and/or splitters 130 that pass the optical signalto a main detector 140. As used herein, a coupler is typically a fiber(e.g., multimode fiber) for guiding light whereas a splitter typicallyutilizes a lens and/or mirrors to guide the light. Output from the maindetector 140 is passed to the modem 110 as an electrical signal wherereceiver data is processed and sent as an output to othercomputing/network devices (not shown). A transmitter amplifier 150receives transmitter data from the modem 110 and transmits opticalsignals having modulated transmitter data via the coupler/splitters 130and transceiver optics 120 to a remote optical transceiver (not shown).

The modem 110 transmits outgoing communications data and receivesincoming communications data in the optical communications system 100which can also be referred to as an optical transceiver. The maindetector 140 is coupled to the modem 110 and converts an optical signalrepresenting the incoming communications data to an electrical signalfor the modem. An adaptive data rate processor 160 periodically monitorsthe electrical signal from the main detector 140 to determine a currentpower level for the optical signal. Based on the monitoring, theadaptive data rate processor 160 dynamically adjusts a data rate of themodem based on the current power level of the optical signal.

Atmospheric conditions are periodically monitored via the electricalsignal output of the main detector 140 to determine the strength ofreceived optical signals. During clear line-of-sight conditions betweenthe remote optical transmitter (not shown) and local receiver depictedas part of the system 100, optical signal strength can be stronger(e.g., higher signal-to-noise) than when fading conditions cause thesignal strength to degrade. The adaptive data rate processor 160monitors incoming signal strength and can dynamically increase ordecrease communications data rate of the modem 110 based on detection ofthe current signal conditions. For example, under strong signalconditions, data rate can be dynamically increased to accommodatefavorable conditions and improve communications throughput. When weaksignal conditions are detected (e.g., due to fading and/or distancelimitations), data rate of the modem 110 can automatically be reduced bythe adaptive data rate processor 160 to mitigate loss of data. Theadaptive data rate processor 160 can be substantially any type ofcomputing device and/or controller. This can include microprocessors,computers, microcontrollers, or controllers such as a programmable logiccontroller (PLC), for example. Such devices can be equipped withanalog-to-digital (A/D) converters to monitor the various signalsdescribed herein.

As shown, the adaptive data rate processor 160 can include a controloutput 170 (or outputs) to dynamically adjust a sensitivity level of themain detector 140. For example, the adaptive data rate processor 160 canvary the control output 170 to operate the main detector 140 in a rangebetween high sensitivity for weak optical signals to low sensitivity forstrong optical signals. In one specific example, the adaptive data rateprocessor 160 employs the control output 170 to dynamically adjust abias voltage on the main detector 140 and to dynamically adjust thesensitivity level of the main detector 140. For example, the maindetector 140 can be an avalanche photo diode (APD) that operates betweena range of Geiger mode for high sensitivity (e.g., single photondetection) and low bias mode for low sensitivity. The adaptive data rateprocessor 160 in this example dynamically adjusts the reverse biasvoltage on the APD via control output 170 to select the sensitivitymode. The adaptive data rate processor 160 can include control circuitsthat can be analog or digital or combinations thereof. Such circuits caninclude microprocessors, microcontrollers, or controllers that executecomputer-executable instructions to dynamically adjust sensitivitylevels. In another example, discrete hardware control circuits includinganalog and/or digital components can be employed.

When an optical power level change has been detected by the adaptivedata rate processor 160 by monitoring the main detector 140, theadaptive data rate processor 160 notifies the modem 110 to change itsdata rate in response to the detected power level change. Also, theadaptive data rate processor 160 can dynamically adjust the sensitivitylevel of the main detector 140 via the control output 170 based on thedetected power level change. In one example of synchronous data ratechange between the system 100 and the remote transceiver, the modem 110can transmit a packet of data (e.g., header packet) indicating a datarate change to the optical transmitter 150 that communicates the datarate change to the remote transceiver based on a command from theadaptive data rate processor 160. For instance, the modem 110 cannegotiate a new data rate with the remote transceiver by exchanging datapackets that indicate the new data rate. After successful negotiation,both the modem 110 and a modem operating at the remote transceiver canadjust their respective data rates accordingly (e.g., lower data ratesfor weak optical signals due to fading and high data rates for strongsignal conditions). As used herein data rate can be defined as a numberof bits per second or commonly referred to as baud rate.

In another example of asynchronous data rate change between the system100 and the remote transceiver, it can be assumed in some cases thatboth the system 100 and the remote transceiver system detect similarchanges in optical power levels in a concurrent manner. In such a case,the adaptive data rate processor 160 can command the modem 110 to a newdata rate based upon detecting a power level change from the currentpower level where the new data rate is based upon a predetermined powerthreshold. For example, if the optical power level has been detected tohave dropped by 10 db but not more than 20 db, the adaptive data rateprocessor 160 can command the modem 110 to adjust its current data rateto a predetermined data rate associated with the detected power levelchange. Both the modem 110 and remote modem at the remote transceivercan wait a predetermined time period, if necessary, before resumingcommunications based on the new data rate and detected power level.

In another example, the adaptive data rate processor 160 can dynamicallyadjust the data rate based upon system mode. For example, the systemmode can include a coarse-mode for pointing where transmitter andreceiver terminals are directed to search for other communicatingterminals. The system mode can include a mid-mode for acquisition wherethe transmitter and receiver terminals are localized to a region. Yetanother system mode can include a tracking-mode where the transmitterand receiver terminal have locked positions for transmitting andreceiving data between the terminals. The adaptive data rate processor160 can dynamically adjust the data rate if tracking between theterminals during the tracking mode degrades to support reentry into thecoarse-mode or the mid-mode, where the data rate may have to decreasefor example to support reentry into one or more of the other systemmodes.

In another example, the adaptive data rate processor 160 can dynamicallyadjust the data rate based upon an estimated bit error rate (BER). Also,the adaptive data rate processor 160 can dynamically adjust the datarate independently between a header portion and a data portion of a datapacket. This includes dynamically adjusting the data rate independentlyfor transmitted data packets while receiving data packets with differentinformation rates from the transmitted data packets, for example. Inanother example, the adaptive data rate processor 160 can dynamicallyadjust the data rate by repeating bits in a redundant pattern within aheader portion or a data portion of a data packet to signal an increaseor a decrease in the data rate. For example, normal data transmissionsmay include an alternating pattern of 1, 0, [data bit], 1, 0, [data bit]and so forth. If the alternating packet is instead repeated such as 111,000, for example, the receiving terminal can deduce that a data ratechange should occur. The receiver of the data packet can thus sense theredundant pattern to dynamically increase or decrease the data rate. Inone other example, the system 100 can include a separate communicationschannel (not shown) that is established between transmitter and receiverterminals to negotiate data rate changes. The separate communicationschannel can include at least one of an electrical link, a radiofrequency (RF) link, and a fiber optic link, for example.

Various configurations are possible for the system 100 depending onconfiguration of the transceiver optics 120 and coupler/splitters 130.For example, the transceiver optics 120 can include a first aperture totransmit or receive the optical signal to or from the remotetransceiver. In another example, a second aperture can be employed totransmit or receive the optical signal to or from the remotetransceiver. Thus, one aperture can be employed to transmit optical dataand the second aperture can be employed receive optical data. Thecoupler/splitters 130 can include a first free space to fiber coupler tocouple the optical signal from the first aperture to an optical receiverfiber and a second free space to fiber coupler to couple the opticalsignal from a transmitter fiber to the second aperture. Yet anothercoupler in the coupler/splitters 130 can include a power coupler tocouple the optical signal from the receiver fiber to the main detector140. FIG. 3 described below illustrates further examples of theapertures and couplers described herein.

In yet another example configuration (See FIG. 4 ), an auxiliarydetector can be employed to detect power level changes by the adaptivedata rate processor 160 while the main detector 140 is utilized toreceive optical data and convert the optical data to electrical data atthe modem 110. The adaptive data rate processor 160 can dynamicallyadjust the data rate of the modem 110 based on the signal detected fromthe auxiliary detector. In the auxiliary detector example, the adaptivedata rate processor 160 can also dynamically adjust the sensitivity ofboth the main detector 140 and the auxiliary detector to further improvecommunications performance.

FIG. 2 illustrates an example diagram 200 of received optical powerlevels that can be monitored by an adaptive data rate processor todynamically adjust a data rate or a sensitivity level of an opticaltransceiver. The diagram 200 depicts optical power levels that vary overtime captured at 8.2 seconds on the left to 8.7 seconds on the right ofthe horizontal axis. The vertical axis of the diagram 200 representspower level changes from −20 db at the bottom to plus 5 db at the top.The optical power signal depicted in the diagram 200 was captured atabout a distance of 4.2 kilometers between transmitter and receiver. Asshown, an example fade at 210 can last for a period of about 12.5milliseconds, whereas an example power burst at 220 lasts for about 15milliseconds.

Such periods of burst and fading typically last for much longerintervals than the modulated data rate which can be on the order of 10'sof gigabits per second. As such, the power signal can be analyzed by theadaptive data rate processor described above to determine when periodsof fading or bursting have occurred and adjust date rates or sensitivitylevels of the transceiver accordingly. For example, a slope analysis ofthe optical power signal along with analyzing how high or low the powersignal has ascended or descended can be utilized to detect when thepower levels have changed enough (e.g., beyond a predetermine threshold)such that a data rate and/or sensitivity level change ought to occur.Other mathematical functions such as averaging, derivatives, andintegrals, for example, can be employed to analyze the respective powersignal. As can be appreciated, the optical power signal depicted in thediagram 200 is but one example of a plurality of different transmittingand receiving conditions that are possible which would affect the shapeand magnitude of the signal depicted in the diagram 200.

FIG. 3 illustrates an example of an optical communications system 300that employs separate transmitter and receiver paths to dynamically varythe communications data rate of a modulator/demodulator (modem) 310based upon detected optical power levels. As shown, the modem 310transmits transmitter data via a transmitter optical amplifier 320 thatcouples to a free space to fiber coupler 324 which couples opticalsignal to an aperture 330 which drives an optical output to a remotetransceiver (not shown). In contrast to the system depicted in FIG. 1 ,the system 300 employs separate receiver optics and couplers for thetransmitter path and the receiver path of the system 300. With respectto optical signal input from the remote transceiver, the system 300includes a second aperture 340 that couples the received optical signalto a second free space to fiber coupler 344. The apertures 330 and 340can include telescopic components for transmitting and/or receivingoptical data over a distance. Output from the coupler 344 is fed to apower coupler 350 which drives a main detector 360. The main detector360 converts optical data to electrical data for the modem 310 andprovides a power input to an adaptive data rate processor 370 todynamically adjust the data rate to the modem 310 in view of detectedpower levels. As noted above, the adaptive data rate processor 370 canalso dynamically adjust the sensitivity level of the main detector 360based on the detected power levels from the main detector.

FIG. 4 illustrates an example of an optical communications system 400that employs an auxiliary detector 408 to dynamically vary thecommunications data rate of a modulator/demodulator (modem) 410 basedupon detected optical power levels. Similar to the system 300 of FIG. 3, the modem 410 transmits transmitter data via a transmitter opticalamplifier 420 that couples to a free space to fiber coupler 424 whichcouples optical signal to an aperture 430 which drives an optical outputto a remote transceiver (not shown). In contrast to the system depictedin FIG. 1 , the system 400 employs separate receiver optics and couplersfor the transmitter path and the receiver path of the system 400. Withrespect to optical signal input from the remote transceiver, the system400 includes a second aperture 440 that couples the received opticalsignal to a second free space to fiber coupler 444. The apertures 430and 440 can include telescopic components for transmitting and/orreceiving optical data over a distance. Output from the coupler 444 isfed to a power coupler 450 which drives a main detector 460 and theauxiliary detector 408. The main detector 460 converts optical data toelectrical data for the modem 410.

The auxiliary detector 408 can be employed to detect power level changesby an adaptive data rate processor 460 while the main detector 440 isutilized to receive optical data and convert the optical data toelectrical data at the modem 410. The adaptive data rate processor 470can dynamically adjust the data rate of the modem 410 based on thesignal detected from the auxiliary detector 408. The adaptive data rateprocessor 470 can also dynamically adjust the sensitivity of both themain detector 460 and/or the auxiliary detector 408 to further improvecommunications performance.

In view of the foregoing structural and functional features describedabove, a methodology in accordance with various aspects of the presentinvention will be better appreciated with reference to FIG. 5 . While,for purposes of simplicity of explanation, the methodology of FIG. 5 isshown and described as executing serially, it is to be understood andappreciated that the present invention is not limited by the illustratedorder, as some aspects could, in accordance with the present invention,occur in different orders and/or concurrently with other aspects fromthat shown and described herein. Moreover, not all illustrated featuresmay be required to implement a methodology in accordance with an aspectof the present invention. The various acts of the method depicted inFIG. 5 can be executed automatically such as via a processor, computer,and/or controller configured with executable instructions to carry outthe various acts described herein. Moreover, discrete circuit controlimplementations are possible in addition to hybrid controls that includeboth discrete and integrated circuit processing elements.

As noted previously, the adaptive data rate processor 470 candynamically adjust the data rate based upon system mode. For example,the system mode can include a coarse-mode where transmitter and receiverterminals are directed to search for other communicating terminals. Thesystem mode can include a mid-mode for acquisition where the transmitterand receiver terminals are localized to a region. Yet another systemmode can include a tracking-mode where the transmitter and receiverterminal have locked positions for transmitting and receiving databetween the terminals. The adaptive data rate processor 470 candynamically adjust the data rate if tracking between the terminalsduring the tracking mode degrades to support reentry into thecoarse-mode or the mid-mode, where the data rate may have to decreasefor example to support reentry into one or more of the other systemmodes.

In another example, the adaptive data rate processor 470 can dynamicallyadjust the data rate based upon an estimated bit error rate (BER). Also,the adaptive data rate processor 470 can dynamically adjust the datarate independently between a header portion and a data portion of a datapacket. This includes dynamically adjusting the data rate independentlyfor transmitted data packets while receiving data packets with differentinformation rates from the transmitted data packets, for example. Inanother example, the adaptive data rate processor 470 can dynamicallyadjust the data rate by repeating bits in a redundant pattern within aheader portion or a data portion of a data packet to signal an increaseor a decrease in the data rate. For example, normal data transmissionsmay include an alternating pattern of 1, 0, [data bit], 1, 0, [data bit]and so forth. If the alternating packet is instead repeated such as 111,000, for example, the receiving terminal can deduce that a data ratechange should occur. The receiver of the data packet can thus sense theredundant pattern to dynamically increase or decrease the data rate. Inone other example, the system 400 can include a separate communicationschannel (not shown) that is established between transmitter and receiverterminals to negotiate data rate changes. The separate communicationschannel can include at least one of an electrical link, a radiofrequency (RF) link, and a fiber optic link, for example.

FIG. 5 illustrates an example of an optical communications method 500that dynamically varies the communications data rate of an opticaltransceiver based upon detected optical power levels. At 510, the method500 includes detecting (e.g., by a processor) a current power level of areceived optical signal in an optical transceiver (e.g., via maindetector 140 and adaptive rate processor 160 of FIG. 1 ). At 520, adetermination is made regarding whether or not an optical power levelhas changed (e.g., via adaptive data processor 160 of FIG. 1 ). If thecurrent power level has not changed from a previous power level at 520,the method proceeds to 530 and continues proceeds with current modemcommunications data rates. The method 500 can periodically proceed backto 510 to detect incoming power levels (e.g., during an interruptroutine).

At 540, the method 500 determines a new data rate (e.g., via adaptivedata rate processor 160 of FIG. 1 ). The new data rate can be computedby comparing the current power level (or slope) to predetermined powerthresholds for example. This could also include comparing to a powersignature for a respective communications channel. At 550, the method500 adjusts a data rate for the optical transceiver if the current powerlevel of the received optical signal has changed from the previous powerlevel as detected at 520 (e.g., via adaptive data rate processor 160 ofFIG. 1 ). At 560, the method 500 adjusts a sensitivity level of at leastone detector in the optical transceiver if the current power level ofthe received optical signal has changed from the previous power level(e.g., via control output 170 of FIG. 1 ). At 570, the method 500includes syncing the new data rate with a remote transceiver based onthe determined new data rate. This can include synchronous negotiationswith the remote transceiver such as via a header packet that istransmitted to the remote transceiver to confirm the change of the newdata rate.

In another example, asynchronous data rate changes could also beemployed for example, where both local and remote transceivers couldmutually change their respective data rates based upon detected powerlevels and predetermined power thresholds at each end of thecommunications path. A delay period could also be initiated at each endwhile each transceiver adjusts its respective data rate. At 580, themethod 500 verifies the communications channel between the remote andlocal transceiver (e.g., via modem 110 of FIG. 1 ). This can includeexchanging one or more data packets to confirm that the new data ratehas been communicated and changed at the remote transceiver. After thedata rate has been changed at 580, the method 500 proceeds back to 530for further modem communications.

What have been described above are examples. It is, of course, notpossible to describe every conceivable combination of components ormethodologies, but one of ordinary skill in the art will recognize thatmany further combinations and permutations are possible. Accordingly,the disclosure is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims. As used herein, the term“includes” means includes but not limited to, the term “including” meansincluding but not limited to. The term “based on” means based at leastin part on. Additionally, where the disclosure or claims recite “a,”“an,” “a first,” or “another” element, or the equivalent thereof, itshould be interpreted to include one or more than one such element,neither requiring nor excluding two or more such elements.

What is claimed is:
 1. An optical communications method comprising:detecting, by a processor, a current power level of a received opticalsignal in an optical transceiver; determining, by the processor, if thecurrent power level of the received optical signal has changed from aprevious power level; adjusting, by the processor, a data rate for theoptical transceiver to a new data rate based on the current power levelof the received optical signal having changed from the previous powerlevel, wherein the new data rate is based upon a predetermined powerthreshold; and adjusting, by the processor, a sensitivity level of atleast one detector and a bit rate of a modem in the optical transceiverbased on the current power level of the received optical signal havingchanged from the previous power level.
 2. The method of claim 1, furthercomprising transmitting a packet of data indicating the adjustment ofthe data rate via a line-of-sight path to a remote transceiver.
 3. Themethod of claim 1, further comprising the processor asserting a controloutput to dynamically adjust the sensitivity level of the at least onedetector.
 4. The method of claim 3, further comprising the processoremploying the control output to dynamically adjust a bias voltage on theat least one detector to adjust the sensitivity level of the at leastone detector.
 5. The method of claim 1, further comprising the modemtransmitting a packet of data indicating the adjustment of the data rateto an optical transmitter that communicates the adjustment of the datarate to a remote transceiver based on a command from the processor. 6.The method of claim 1, further comprising detecting, with auxiliarydetector that is distinct from the at least one detector, a power levelof the optical signal and generating an electrical output signalrepresenting the power level.
 7. The method of claim 6, wherein theauxiliary detector is an avalanche photo diode (APD) that operatesbetween a range of Geiger mode for high sensitivity and low bias modefor low sensitivity, wherein the processor dynamically adjusts a reversebias voltage on the APD to select Geiger mode, low bias mode ortherebetween.
 8. An optical communications method comprising: receivingan optical signal with both a main detector and an auxiliary detector ofan optical transceiver; detecting, by a processor, a current power levelof the optical signal as received by the auxiliary detector, andgenerating an electrical output signal representing the power level;determining, by the processor, if the current power level of thereceived optical signal has changed from a previous power level of theoptical signal as received by the auxiliary detector; adjusting, by theprocessor, a data rate for the optical transceiver based on the currentpower level of the received optical signal having changed from theprevious power level; and adjusting, by the processor, a sensitivitylevel of the main detector and a bit rate of a modem in the opticaltransceiver based on the current power level of the received opticalsignal having changed from the previous power level.
 9. The method ofclaim 8, further comprising transmitting a packet of data indicating theadjustment of the data rate via a line-of-sight path to a remotetransceiver.
 10. The method of claim 9, wherein the auxiliary detectoris an avalanche photo diode (APD) that operates between a range ofGeiger mode for high sensitivity and low bias mode for low sensitivity,wherein the processor dynamically adjusts a reverse bias voltage on theAPD to select Geiger mode, low bias mode or therebetween.
 11. The methodof claim 8, further comprising: the processor asserting a control outputto dynamically adjust the sensitivity level of the main detector; andthe processor employing the control output to dynamically adjust a biasvoltage on the main detector to adjust the sensitivity level of the maindetector.
 12. The method of claim 8, further comprising the modemtransmitting a packet of data indicating the adjustment of the data rateto an optical transmitter that communicates the adjustment of the datarate to a remote transceiver based on a command from the processor. 13.The method of claim 8, further comprising the processor dynamicallyadjusting the data rate based upon a system mode.
 14. The method ofclaim 13, wherein the system mode includes a coarse pointing mode wheretransmitter and receiver terminals are directed to search for othercommunicating terminals, a mid-mode for acquisition where thetransmitter and receiver terminals are localized to a region, and atracking mode where the transmitter and receiver terminal have lockedpositions for transmitting and receiving data between the terminals. 15.An optical communications method comprising: detecting, by an adaptivedata rate processor, a current power level of a received optical signalin an optical transceiver; determining, by the adaptive data rateprocessor, if the current power level of the received optical signal haschanged from a previous power level; dynamically adjusting, by theadaptive data rate processor, a data rate for the optical transceiverbased on the current power level of the received optical signal havingchanged from the previous power level, and further based on a systemmode; and adjusting, by the adaptive data rate processor, a sensitivitylevel of at least one detector and a bit rate of a modem in the opticaltransceiver based on the current power level of the received opticalsignal having changed from the previous power level.
 16. The method ofclaim 15, further comprising transmitting a packet of data indicatingthe adjustment of the data rate via a line-of-sight path to a remotetransceiver.
 17. The method of claim 16, wherein the system modeincludes a coarse pointing mode where transmitter and receiver terminalsare directed to search for other communicating terminals, a mid-mode foracquisition where the transmitter and receiver terminals are localizedto a region, and a tracking mode where the transmitter and receiverterminal have locked positions for transmitting and receiving databetween the terminals.
 18. The method of claim 17, further comprisingthe adaptive data rate processor dynamically adjusting the data ratebased on tracking between the terminals during the tracking modedegrading to support reentry into the coarse pointing mode or themid-mode.
 19. The method of claim 15, further comprising the adaptivedata rate processor asserting a control output to dynamically adjust thesensitivity level of the at least one detector.
 20. The method of claim19, further comprising the adaptive data rate processor employing thecontrol output to dynamically adjust a bias voltage on the at least onedetector to adjust the sensitivity level of the at least one detector.